a) Dairy Operation Background
In general, the invention is a system for recovering manure in a diary operation or other environments where manure is recovered for purposes of supplying a digester or other practical use. In one form the implementation can be executed on an existing dairy facility that employs a flush system to remove the manure from the stalls or a location containing cows.
Many dairy systems struggle with conflicting criteria and various portions of their diary operation. When a dairy employs a digester for extraction of energy from biodegradable material which is contained in settleable and unsettleable solids, it is desirable to feed a digester at a fairly high concentration of this biodegradable material. In general, the biodegradable material can generally be classified as a settleable solid or as unsettleable solids. A settleable solid is adapted to be removed by a settling process with a tank. An unsettleable solid contains very fine particular matter or dissolved solids which are not adapted to be removed by any form of settling process without chemical coagulants.
Therefore, it is desirable to feed a digester with settleable and unsettleable solids at a sufficiently high percentage rate with respect to the water to reduce the amount of cost for the size of the digester and the ongoing costs of maintaining such as heating the fluid and solid mixture contained therein.
The dairyman has another criteria for the flush system where it is desirable to have the unsettleable contact (as well as settleable content) within the flush system kept to a minimum. In general, the biodegradable material to feed a digester is all retrieved from the flush system of the dairy. The flush system requires water as the operating medium to flush out the stalls of the dairy containing a material as well as manure and an assortment of other solids. Generally a flush system is a partial close loop system where the flush water is recycled to some degree. Oftentimes it is desirable to add an injection of water to dilute the amount of unsettleable material contained in the partially closed loop system.
The addition of water is normally problematic for the digester whereby it adds further cost for removal of the water or alternatively the digester must be made larger to accommodate a lower concentration of solids. Alternatively in the worst-case scenario, the digester may not function properly at all because the solid content is at such a low percentage.
Therefore, prior to the system described herein, the dairy was forced to either compromise the purity of the flush water by having a higher concentration of unsettleable solids or have excessive cost of building and maintaining a digester which has to process a watered down lower percentage of biodegradable material.
b) General Background of Invention
Depending upon the dairy, certain material flushed with the flush water settles better and of course ranges of flush rates and flush water per day varies immensely. For example, depending upon the flush system in the dairy, the flush intervals, the bedding material in the dairy and other factors all determine the settling rates of the settleable material. Present observation indicates that the settling rates vary a substantial amount from dairy to dairy.
In general, the system described herein employs a novel topography of components adapted to pass a large volume of fluid through the system yet have the ability to recover settleable solids therefrom while maintaining a low percentage of unsettleable solids in the recirculating flush water.
Prior art systems incorporate a first separator that feeds a process tank. Fluid is taken from the process tank and is used to flush the dairy in a partial closed loop system. The system is partial closed loop because new solid material is always being added during the flush and material leaves the system in the process tank. A certain amount of unsettleable solids come out of the dairy everyday. The unsettleable solids are similar as dissolved solids but further include fine suspended solids and these fine suspended solids as well as dissolved solids are referred to as unsettleable solids. These unsettleable solids exit in solution at the bottom portion of a process tank. The amount of water added at the flush must equal the amount of water exiting the closed loop system.
For example, if 1000 lbs. of unsettleable solids enter the system a day and 990,000 lbs. of water is in the closed loop system, the level of unsettleables will build to 10,000 lbs. in ten days which is 1% unsettleable solid content in the partial closed loop system by weight. Therefore, removing a portion of the fluid in the close looped flush system is desirable to removing the unsettleable solids. Therefore, if approximately 100,000 lbs. of water and unsettleable solids are removed from the close loop system per day, 1% of the 100,000 lbs. would include 1000 lbs. of unsettleable solids which approximately is the amount of unsettleable solids added to the partially closed loop system. Therefore, per day, the system is in equilibrium; however, 100,000 lbs. of fresh water must be added to the partial closed loop system and the 100,000 lbs. of exiting water and solids must be processed.
Having more water in the system, in general, is helpful to keeping the unsettleable solids level low. Therefore, the system described herein allows for lowering the content of unsettleables solids that are in the close looped flush region and further having the ability to extract settleable solids therefrom. By having a large quantity of flush water and running more fluid through eh system, the system is actually advantageous to removing the unsettleable solids.
Using the example above, let us say it is desirable in a certain application to keep the flush water below 1% of unsettleables solids which appears as clean translucent water without visible particles. In the broader range, between 0.5% and 2% of unsettleable solids is acceptable for certain flush dairy situations. In general dairies have such a variety of amounts of unsettleables, the published literature on solids in dairy flush system in scarce relating to the content of solids that are settleable and unsettleable. This is likely because the amounts vary tremendously from dairy to dairy. A greater input of water in come cases requires larger and more thickening tanks descried further herein.
In the system described below, the flush water from the dairy passes through a separator to a process tank having the bottom removal system by head pressure. This is a feature where prior art tends to employ pumps have bottom removed for 30 seconds every seven minutes for example. The starting and stopping of the pumps cause for wear on the equipment and potential noise pollution.
Bottom removal of the processed tank can be done between once every half-hour to once every two hours depending upon the thickening tank, settling rate, continuous flush versus batch flush and other factors. For example, a 2000 cow dairy that flushes eight lanes which flushes each lane for 10 minutes and then has no flushing for four hours would be more of a batch style flushing system. Such a system would need to coordinate with the processing tank to bottom remove solids after a sufficient time is allowed for settling.
Prior art methods of bottom removal generally do so in a low fluid flow manner. An aspect of the removal descried below is a bottom removal process at a high-volume burst. In the system described below some turbulence is desirable to facilitate the removal. Thereafter, the bottom removal in the process tank is ceased to allow for additional and further settling. It has been found that a burst of high volumetric flow removes the solids sufficiently. For example, if there are 1.5 inches of solids in the bottom of the tank the timing is such to burst the solid region out and remove 2 to 3 in. of water and settleables at the bottom. The one and a half inches of chase water is used to help remove the unsettleables. The bottom 1.5 inches for example could be 5% solids and the top 1.5 inches could be one half percent solids on average. Therefore, as described in the first example above, the dairy must take out a certain amount of water which is more than the height of the solid layer in the bottom of the process tank. The bottom removed effluent from the process tank is directed to one or one of a plurality of thickening tanks.
The thickening tanks are adapted to receive the bursted fluid from the process tank in a batch like process. Prior art systems relating to management of solids from a flush system include incorporate settling cells. In general, settling cells are large concrete open structures that are adapted to have effluent from either a prior art processing tank or directly from a first separator receiving flush water from the dairy. However, the fluid and solid mixture flowing through settling cells did not provide a steady substantially still environment to facilitate and promote settling of the settleable materials contained therein. The management of settlement cells and consistency of the solids contained therein is generally problematic and time-consuming. Further, solids from settling cells are delayed to getting into a digester or other forms of use. When the settling cells are in operation, they may fill with solids over the period of a week and when one is full, the transfer of effluent from a process tank would then occur to another settling cell. Weather conditions have an impact and are a causal factor to the lack of consistency of results of the solids in the settling cells. Further, as the manure sits in settling cells exposed to the environment, the biological material contained therein is undergoing a natural breakdown by various organisms and hence not capturing energy contained therein and further there are various odor considerations. The anaerobic and aerobic activity is problematic causing various foul odors that are oftentimes unpleasing to neighboring properties. Some settling cells are large and it may be months before managing them therefore amplifing the problems associated therewith.
The thickening tanks as recited herein are enclosed and adapted to pass fluid as well as solids therethrough the system. Further, the thickening tanks are adapted to remove fluid from the process tank which inherently removes dissolved and unsettleable solids contained therein to fluid.
For example, a 7000 to 8000 cow dairy may have two, three or four 10,000 gallon thickening tanks depending upon the numerous parameters dictating the flushing system of the dairy. Let us say in one embodiment that a dairyman has three 10,000 gallon thickening tanks labeled A, B and C that are adapted to receive fluid intermittently from the process tank. Therefore, the process of filling the tanks will be to fill the first tank A in the first hour. Thereafter sometime during the second hour tank B will be filled from the process tank in a batch like operation. In the third hour tank C is filled from the process tank and during this hour the material from tank A is removed in a two-step process where the first 30 minutes may be used to decant at the upper portion of fluid and the second 30 minutes are used to bottom remove the fluid containing solids. Therefore, tank A will have almost two hours of settling time. It should be noted that the thickening tank creates 100% still environment where there is not fluid entering the tank stirring up the settled material after it is filled.
Prior art devices adapted to feed a digester discourage the use of excess water. A dairyman desires a fresh input of water to reduce the amount of settleables (as well as unsettleables, that comprise the solids in the fluid) contained in the flush water and hence such larger quantities is not conductive for use with a digester. However, the system provided below allows for recovery of a large amount of solids from flush water in a concentrated form and provides for flush water that is pure with a reduced amount of unsettleable solid content contained therein.